1. Field of the Invention
The present invention relates to a digital camera, and particularly relates to the digital camera having a perspective control function that changes perspective of an image and adjusts visibility on an electronic display so as to photograph the image, and that prevents dust from adhering to an image pickup element.
2. Description of the Related Art
As shown in FIG. 7A, in the case where an entire object 71 such as high building or construction is tried to be photographed by a camera 72, when the camera 72 to be used is normal, an optical axis L of a photographing lens 73 necessarily faces upward. FIG. 7B illustrates the case where relative position relationship between the camera 72 and the object 71 shown in FIG. 7A is constant and the optical axis L of the photographing lens 73 is horizontal. As is clear from FIG. 7B, the image of the object 71 photographed in such a state is seem to tilt backward.
FIG. 8 is an one example which is obtained by schematizing the picture photographed in the state of FIGS. 7A and 7B. For example, in the case where a tower block or the like with constant width which is long in an up-down direction is the object 71, an upper part of the object 71 (far portion) seems to have a narrow width and a lower part (near portion) seems to have a wide width. Further, the entire object 71 seems to tilt backward, and tower blocks on the right and left sides in FIG. 8 seem to tilt inward.
In order to solve a problem of deformation of an object due to the perspective, a digital camera that makes digital correction by means of a processor that stores photographed images in the camera is proposed (for example, see Japanese Patent Application Laid-Open No. 2002-335438 corresponding to U.S. Pat. No. 6,963,365 (Patent Document 1)).
The conventional example disclosed in Patent Document 1, however, has the following problem. That is to say, firstly, an operation of the camera becomes very complicated. Secondary, when perspective is controlled by a post-process, a pulse rate is partially changed, and thus the quality of an image is consequentially deteriorated. Thirdly, since an image to be displayed on a monitor at the time of photographing is an uncorrected image, a finally frame or the like cannot be checked at the time of photographing. Further, a finished state after the post-process cannot be imaged at the time of photographing. If photographing is failed, a correction cannot be mostly made by the post-process. From these points, it is not preferable that the perspective is electronically controlled in the post-process except that emergency evacuation (a failed picture is saved).
The perspective control may be made, as shown in FIG. 9, by making a surface of a film (image pickup element) 92 parallel with a surface of the object 71, and moving an optical axis L of a photographing lens 93 to a vertical direction within a range that the object is imaged satisfactorily in an image frame of the film 92 so as to adjusting a position. This perspective control is already made in view cameras or the like, and this is described in [0003] to [0004] of Patent Document 1.
In the case of modernized rigid cameras, however, the perspective control becomes gradually difficult and thus is actually omitted. For example, in range finder type cameras, the perspective control becomes difficult and then disabled. The perspective control is revived in single lens reflex cameras, but since special lenses should be used, they become very expensive and are not practical (see [0003] of Patent Document 1).
Meanwhile, lens interchangeable type digital cameras come onto the market. The biggest problem of the lens interchangeable (attachment/detachment) type digital cameras is that dust adheres to image pickup elements, but some of such cameras on the market have a constitution such that lowpass filter etc. provided just in front of the image pickup element is ultrasonically vibrated by crystal resonator so that the dust adhering to the filter is shaken off, and the dust is collected using pressure sensitive adhesive so that re-flying of the dust is prevented. Further, digital cameras provided with wiper for wiping the image pickup elements come onto some markets. These cameras, however, do not have the complete dust-proof function.
Lenses for the perspective control in single-lens reflex cameras are very expensive, and their position can be adjust positions only to a single direction due to their constitution. If, however, the state shown in FIG. 7A is a plan view, the position adjustment is necessary also for a horizontal direction (right-left direction). In many photographing cases, the positions should be actually adjusted to both directions: an up-down, namely, vertical direction (longitudinal direction) and a right-left, namely, horizontal direction (lateral direction) which is perpendicular to the vertical direction. In the case of the single-lens reflex cameras, since the position can be adjusted only to a single direction, a vicinity of a mounting base portion of the lens can be rotated. In actual photographing, therefore, it is not easy to determine the final position.
In order to realize the state shown in FIG. 9, the optical axis of the lens may be constituted so as to be capable of moving relatively with respect to the film or a center of the image pickup element. It is, therefore, easier that the optical axis of the lens is fixed to the camera, and the film or the image pickup element is moved. In the case of the single-lens reflex cameras, however, it is necessary that a position relationship between a photographing screen of the film or the image pickup element and a focusing glass for observing a photographing state is an equivalent position such that they are symmetrical at 90° (occasionally including any angles other than 90°), for example. For this reason, it is actually impossible that the film or the image pickup element is moved in order to make the perspective control.
Recent electronic displays have notably high definition, and optical finders are replaced by electronic view finders for practical use. The electronic finder, therefore, gets free from a constitution that it establishes a constant relationship with an image pickup element in the installation position of camera. For this reason, a photographing lens is fixed and the image pickup element is moved to the vertical direction with respect to the optical axis of the photographing lens, so that the perspective control becomes practical.
With particularly ferroelectric liquid crystal which is developed recently, a circuit is formed directly on silicon, pixel pitch of 10μ and resolution of 2500 dip are realized, and an aperture ratio is high so that meshes between pixels are hardly sensed. Further, since responsibility is very high (100 to 10 μsec which is about 1000 times as high as that of conventional liquid crystal displays), time-division display (high-frequency time division does not cause color burst in motion picture images) is enabled, and these characteristics are synthesized so that micromini size and high definition are realized. Since the ferroelectric micro-displays have very small screen size, the displays cannot be directly viewed, and thus they are enlarged to be viewed by an ocular magnifying glass.
The digital cameras having the perspective control function, however, cause a difficult problem at the stages of design and manufacturing. This is because, in order to move an image pickup element at a constant posture, a guide way is normally necessary, and in this case, even very small guide ways require expense and man-hour.
When an image pickup element is actually tried to be constituted so as to be capable of moving and adjusting individually to both lengthwise and lateral directions, two-tiered guide ways are necessary in a direction perpendicular to the longitudinal and lateral directions. Further, it is necessary to mount an image pickup element onto a double slide included in a camera main body having a sealed structure, and enable the image pickup element to move and adjust independently to the longitudinal and lateral directions. In this case, it is necessary to set the image pickup element so as not to improperly move due to external shock or the like at the time of photographing, and thus the constitution becomes complicated.
In the conventional cameras, it is already embodied that lattice-shaped lines are printed or carved on a focusing glass and an image is visually checked. In a state where a structural outline is determined at the time of photographing, the lattice-shaped lines do not match with the image in a positional relationship, and thus it is difficult to observe the state of the perspective.
In order to make the perspective control, an image circle of the photographing lens requires margin, but most of the recent single-lens reflex cameras are designed so as to be capable of using interchangeable lenses of conventional silver halide film cameras. Further, most of the single-lens reflex cameras use image pickup elements whose area is smaller than a standard format 24 mm×36 mm of the conventional silver halide films, but it is convenient that the above lenses and the image pickup elements are combined to be used. This is because the image circle of the photographing lens has margin, and the perspective control is enabled in all interchangeable lenses.
Even if the image circle has margin, however, it is very difficult to make the perspective control in the constitution of the conventional single-lens reflex cameras, but single-lens reflex type (lens interchangeable type) digital cameras have another problem. The problem is that dust enters the cameras at the time of attaching/detaching lenses so as to adhere to the image pickup elements.
In order to solve the above problem, cameras in which lowpass filter etc. provided just in front of the image pickup elements are ultrasonically vibrated so that dust is shaken off, and cameras in which dust is wiped by a wiper come onto the market. Although the structures become complicated and their manufacturing cost is high, the actual dust removing effect is not perfect.